WO2014077197A1

WO2014077197A1 - Biaxially oriented polyester film and method for producing same

Info

Publication number: WO2014077197A1
Application number: PCT/JP2013/080221
Authority: WO
Inventors: 考道後藤; 清水　敏之; 中谷　伊志; 池畠　良知
Original assignee: 東洋紡株式会社
Priority date: 2012-11-16
Filing date: 2013-11-08
Publication date: 2014-05-22
Also published as: JP5994864B2; US20150299406A1; JPWO2014077197A1; MY161714A; KR20150087193A; TWI605927B; KR102071745B1; TW201420316A; US9688826B2

Abstract

Provided are a biaxially oriented polyester film suited to uses for which nylon film and other flexible films have been used, and a method for producing the same. A biaxially oriented polyester film characterized by comprising a polyester resin composition (A) containing 60 mass% or more polybutylene terephthalate, and by having an MD yield point stress of 70 MPa or lower, a TD yield point stress of 70 MPa or lower, an MD breaking strength of 160 MPa or higher, a TD breaking strength of 160 MPa or higher, and an MD and TD breaking elongation of 100% or higher.

Description

Biaxially stretched polyester film and method for producing the same

The present invention relates to a polyester film and a method for producing the same. More specifically, the present invention relates to a polyester film excellent in the balance of impact resistance, flexibility, and mechanical strength, and a method for producing the same, which are suitable for applications in which nylon films and other flexible films have been conventionally used.

Polybutylene terephthalate (hereinafter referred to as PBT) has been used as an engineering plastic since it has excellent gas barrier properties and chemical resistance as well as mechanical properties and impact resistance. In particular, it has a high crystallization speed. Therefore, it is used as a useful material because of its good productivity. However, PBT has a high crystallization speed and has been considered difficult to biaxially stretch. This is because crystallization occurs due to orientation in the stretching process, and stretching becomes difficult.

Therefore, the film was stretched in the TD direction at a stretching ratio of 3.5 times or less, and then stretched in the MD direction at a deformation rate of 100000% / min or more to produce a biaxially stretched PBT film. A technique for producing a film without unevenness has been known (see, for example, Patent Document 1). However, as can be seen from the results of the examples, this conventional technique increases only the deformation speed in the MD direction, so the elongation is low, the transparency and the dimensional stability are poor, and the MD and TD directions are balanced. However, there was a problem that the film was not formed (see, for example, Patent Document 1).

In an unstretched PBT film, a technology has been known that has excellent processing suitability for applications such as drawing for lithium ion battery exteriors by setting the stab displacement to a specific range (for example, (See Patent Document 2).
However, since this conventional technique is unstretched, the orientation of the PBT is weak, and there is a problem that the original characteristics of the PBT cannot be sufficiently extracted from the viewpoint of mechanical characteristics and impact resistance.
On the other hand, in order to make use of the inherent properties of PBT, studies have been made over the past 40 years for the purpose of improving the plane orientation by biaxial stretching and improving the mechanical properties and impact resistance of the film. Some discussions on past PBT films are discussed.

For example, the PBT film formed by using the tubular simultaneous biaxial stretching method so that the breaking strength in four directions is a specific value or more is said to have little anisotropy and excellent mechanical properties and dimensional stability. The technique has been known (for example, refer to Patent Document 3).
However, this conventional technique has a problem that the thickness accuracy is poor due to the manufacturing method and the puncture strength is low because the plane orientation coefficient does not increase.

In addition to PBT, two types of resins, such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), are laminated in turn, each with high rigidity and high dimensional stability and moldability at high temperatures. Has been known (see, for example, Patent Document 4).
However, since this conventional technique has a layer made of a resin such as PET or PEN in addition to PBT, the stretching temperature is stretching at a stretching temperature of PET or PEN having a Tg higher than that of PBT. In addition, the characteristics of the original PBT film are not drawn, and there are two types of resin compositions in the film. It was difficult to use and disadvantageous in terms of economy.

As described above, the conventional biaxially stretched polybutylene terephthalate film did not have sufficient performance for use as a packaging material or a lithium battery exterior material.

Japanese Patent Laid-Open No. 51-146572 JP 2012-77292 A JP 2012-146636 A WO2004 / 108408 publication

The present invention has been made against the background of the problems of the prior art. That is, an object of the present invention is to provide a biaxially stretched polyester film suitable for applications in which nylon films and other flexible films have been used, and a method for producing the same.

The inventor has intensively studied to achieve this object, and as a result, the present invention has been completed.

That is, the present invention comprises a polyester resin composition (A) containing 60% by mass or more of polybutylene terephthalate, MD yield point stress is 70 MPa or less, TD yield point stress is 70 MPa or less, MD breaking strength is 160 MPa or more, A biaxially stretched polyester film characterized in that the TD breaking strength is 160 MPa or more and the MD and TD breaking elongations are 100% or more.

In this case, it is preferable that the polyester resin (A) comprises a polyester resin (B) other than polybutylene terephthalate.

The method for producing a biaxially stretched polyester film is characterized in that it is obtained by biaxially stretching an unstretched polyester sheet having a thickness of 15 to 2500 μm cast after multilayering the same composition into 60 or more layers. Is preferred.

In this case, it is preferable that the unstretched polyester sheet is biaxially stretched after being brought into contact with a chill roll of 20 ° C. or less and cooled.

Furthermore, in this case, it is preferable to biaxially stretch an unstretched polyester sheet having a spherulite diameter of 500 nm or less in the unstretched polyester sheet.

Furthermore, in this case, it is preferable that the ratio between the breaking strength of MD and the breaking strength of TD is 1.5 or less, and the ratio of the breaking elongation of MD and the breaking elongation of TD is 1.5 or less.

Furthermore, in this case, it is preferable to sequentially biaxially stretch the unstretched polyester sheet.

According to the present invention, it is possible to obtain a biaxially stretched polyester film suitable for applications in which nylon films and other flexible films have been used.

Hereinafter, the present invention will be described in detail.

The polyester resin composition (A) used in the present invention contains PBT as a main component, and the PBT content is preferably 60% by mass or more, more preferably 70% by mass or more, and particularly preferably 75% by mass or more. Preferably, it is 80 mass% or more most preferably. If it is less than 60% by mass, impact strength and pinhole resistance are lowered, and the film properties are not sufficient.
PBT used as a main constituent component is preferably 90 mol% or more, more preferably 95 mol% or more, still more preferably 98 mol% or more, and most preferably 100 mol as terephthalic acid as a dicarboxylic acid component. %. As the glycol component, 1,4-butanediol is preferably 90 mol% or more, more preferably 95 mol% or more, still more preferably 97 mol% or more, and most preferably 1,4-butane during polymerization. Except for the by-product produced by the ether bond of the diol, it is not included.

The polyester resin (A) used in the present invention can contain a polyester resin (B) other than PBT for the purpose of adjusting the film forming property during biaxial stretching and the mechanical properties of the obtained film.
As polyester resins (B) other than PBT, in addition to polyester resins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and polypropylene terephthalate (PPT), isophthalic acid, orthophthalic acid, PBT resin copolymerized with dicarboxylic acid such as naphthalenedicarboxylic acid, biphenyldicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, Neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol, It includes PBT resins diol component such as polycarbonate diol is copolymerized.

The addition amount of the polyester resin other than PBT is preferably 40% by mass or less. If the amount of the polyester resin other than PBT exceeds 40% by mass, the mechanical properties as PBT may be impaired, and impact strength, pinhole resistance, and drawability may be insufficient.

Moreover, in order to improve the pinhole resistance at the time of a bending, the polyester-type and polyamide-type elastomer which copolymerized at least any one of the flexible polyether component, the polycarbonate component, and the polyester component can be added as an additive.
The lower limit of the amount of these additives is 0% by mass, and the upper limit is preferably 20% by mass. If it exceeds 20% by mass, the effect may be saturated and transparency may be lowered.

The lower limit of the resin melting temperature is preferably 200 ° C, and if it is lower than 200 ° C, the discharge may become unstable. The upper limit of the resin melting temperature is preferably 320 ° C., and if it exceeds 320 ° C., the resin may be deteriorated.

The polyester resin may contain a conventionally known additive such as a lubricant, a stabilizer, a colorant, an antioxidant, an antistatic agent, and an ultraviolet absorber as necessary.

As the lubricant type, in addition to inorganic lubricants such as silica, calcium carbonate, and alumina, organic lubricants are preferable, silica and calcium carbonate are more preferable, and calcium carbonate is particularly preferable. By these, transparency and slipperiness can be expressed.

The lower limit of the lubricant concentration is preferably 100 ppm, and if it is less than 100 ppm, the slipperiness may be lowered. The upper limit of the lubricant concentration is preferably 20000 ppm, and if it exceeds 20000 ppm, the transparency may be lowered.

A first point of an example of a suitable method for obtaining the film according to the present invention is to cast a raw material having the same composition in multiple layers during casting.
Since PBT has a high crystallization speed, crystallization proceeds even during casting. At this time, when cast as a single layer without forming multiple layers, there is no barrier that can suppress the growth of crystals, so these crystals grow into large spherulites. As a result, the yield stress of the obtained unstretched sheet is high and not only is it easy to break during biaxial stretching, but also the yield stress of the obtained biaxially stretched film is high, resulting in a film with insufficient moldability. End up.
On the other hand, the inventors of the present invention can reduce the stretching stress of the unstretched sheet by laminating the same resin and not only enable stable biaxial stretching, but also the obtained biaxially stretched film has low yield. It has been found that by having a stress, a flexible and high breaking strength film can be obtained.

Although it is speculated about this cause, even when the same resin is laminated, the interface of the layer exists, and the crystallization is accelerated by the interface, while the growth of large crystals beyond the layer is suppressed, It is considered that the size of the spherulite is reduced.
As a specific method for reducing the size of spherulites by multilayering, a general multilayering apparatus (multilayer feed block, static mixer, multilayer multimanifold, etc.) can be used. For example, extrusion of two or more units A method of laminating thermoplastic resins sent from different flow paths using a machine using a field block, a static mixer, a multi-manifold die, or the like can be used. In addition, when multilayering with the same composition as in the present invention, the object of the present invention is achieved by introducing the multilayering apparatus described above into the melt line from the extruder to the die using only one extruder. It is also possible to fulfill.

As a second point of an example of a suitable method for obtaining the film according to the present invention, it is necessary to reduce the crystallinity of the unstretched sheet during casting. As a specific method for this purpose, casting on a chill roll at a low temperature can be mentioned. Moreover, in order to cool the surface which does not contact a chill roll, it is also possible to install a touch roll and to improve cooling efficiency.

The lower limit of the die temperature is preferably 200 ° C. If it is less than the above, the discharge may not be stable and the thickness may be uneven. The upper limit of the die temperature is preferably 350 ° C., and if it exceeds the above, the thickness becomes non-uniform, the resin deteriorates, and the appearance may be poor due to die lip contamination.

The lower limit of the chill roll temperature is preferably −10 ° C., and if it is lower than the above, the effect of suppressing crystallization may be saturated. The upper limit of the chill roll temperature is preferably 20 ° C, and if it exceeds the above, the crystallinity becomes too high and stretching may be difficult. When the temperature of the chill roll is within the above range, it is preferable to reduce the humidity of the environment near the chill roll in order to prevent condensation.

In casting, the surface of the chill roll rises due to the high temperature resin coming into contact with the surface. Normally, the chill roll is cooled by flowing cooling water through the pipe inside, but securing a sufficient amount of cooling water, devising the arrangement of the pipe, performing maintenance so that sludge does not adhere to the pipe, etc. It is necessary to reduce the temperature difference in the width direction. In particular, care should be taken when cooling at low temperatures without using a method such as multilayering.
At this time, the thickness of the unstretched sheet is preferably in the range of 15 to 2500 μm.

Casting in the multilayer structure described above is performed with at least 60 layers, preferably 250 layers or more, more preferably 1000 layers or more. When the number of layers is small, the spherulite size of the unstretched sheet is increased, and the effect of reducing the yield stress of the obtained biaxially stretched film is lost as well as the effect of improving the stretchability is small.
At this time, the spherulite diameter in the unstretched polyester sheet is preferably 500 nm or less.

The lower limit of the specific gravity of the central part of the unstretched polyester sheet is preferably 1.25 g / cm3, and if it is less than the above, the effect of improving stretchability may be saturated. The upper limit of the specific gravity at the center is preferably 1.3 g / cm 3, and if it exceeds the above, the crystallinity becomes too high and stretching may be difficult.

Next, the stretching method will be described. The stretching method can be simultaneous biaxial stretching or sequential biaxial stretching, but in order to increase the piercing strength, it is necessary to increase the plane orientation coefficient, and in that respect, sequential biaxial stretching is preferable.

The lower limit of the stretching temperature in the longitudinal stretching direction (hereinafter referred to as MD) is preferably 40 ° C, more preferably 45 ° C. If it is lower than 40 ° C., breakage may easily occur. The upper limit of the MD stretching temperature is preferably 100 ° C, more preferably 95 ° C. If the temperature exceeds 100 ° C., the orientation is not applied and the mechanical properties may be deteriorated.

The lower limit of the MD draw ratio is preferably 2.5 times, and if it is less than the above, the orientation is not applied, so that the mechanical properties and thickness unevenness may deteriorate. The upper limit of the MD stretching ratio is preferably 5 times, and if it exceeds the above, the effect of improving the mechanical strength and thickness unevenness may be saturated.

The lower limit of the stretching temperature in the transverse stretching direction (hereinafter referred to as TD) is preferably 40 ° C. If it is less than the above, breakage may easily occur. The upper limit of the TD stretching temperature is preferably 100 ° C., and if it exceeds the above, since the orientation is not applied, the mechanical properties may be deteriorated.

The lower limit of the TD stretch ratio is preferably 2.5 times, and if it is less than the above, the orientation is not applied, so that the mechanical properties and thickness unevenness may deteriorate. The upper limit of the TD stretch ratio is preferably 5 times, and if it exceeds the above, the effect of improving the mechanical strength and thickness unevenness may be saturated.

The lower limit of the TD heat setting temperature is preferably 150 ° C., and if it is less than the above, the heat shrinkage rate increases, and displacement or shrinkage may occur during processing. The upper limit of the TD heat setting temperature is preferably 250 ° C. If the temperature exceeds the above, the film will melt, and even if it does not melt, it may become brittle.

The lower limit of the TD relaxation rate is preferably 0.5%, and if it is less than the above, breakage may easily occur during heat setting. The upper limit of the TD relaxation rate is preferably 10%. If the upper limit is exceeded, sagging may occur and thickness unevenness may occur.

The lower limit of the thickness of the biaxially stretched polyester film of the present invention is preferably 3 μm, more preferably 5 μm, and even more preferably 8 μm. If it is less than 3 μm, the strength as a film may be insufficient. The upper limit of the film thickness is preferably 100 μm, more preferably 75 μm, and still more preferably 50 μm. If it exceeds 100 μm, it may become too thick and processing for the purpose of the present invention may be difficult.

The lower limit of the plane orientation coefficient of the biaxially stretched polyester film of the present invention is preferably 0.1, and if it is less than 0.1, the puncture strength, impact strength, etc. may decrease. The upper limit of the plane orientation coefficient is preferably 0.15, and when it exceeds 0.15, productivity may be lowered and flexibility may be lowered. The plane orientation coefficient can be set within the range by the MD magnification and the heat setting temperature. Further, as the stretching method, sequential biaxial stretching, particularly sequential biaxial stretching in which stretching in the MD direction and then stretching in the TD direction is preferable to simultaneous biaxial stretching.

The biaxially stretched polyester film of the present invention is preferably a resin having the same composition throughout the entire thickness direction of the film.
In addition, a layer of another material may be laminated on the biaxially stretched polyester film of the present invention, and as a method thereof, a method of laminating after forming the biaxially stretched polyester film of the present invention, or a method of laminating during film formation Can be mentioned.

(Film characteristics)
In the biaxially stretched polyester film of the present invention, the MD yield stress is preferably 70 MPa or less, more preferably 65 MPa or less, and further preferably 60 MPa or less. If it is less than the above, the film is difficult to stretch, which may be disadvantageous in terms of workability such as drawing after bonding with various sealants.
In the biaxially stretched polyester film of the present invention, the TD yield stress is preferably 70 MPa or less, more preferably 65 MPa or less, and further preferably 60 MPa or less. If it is less than the above, the film is difficult to stretch, which may be disadvantageous in terms of workability such as drawing after bonding with various sealants.

In the biaxially stretched polyester film of the present invention, the lower limit of the MD breaking strength is preferably 160 MPa, more preferably 180 MPa, and further preferably 200 MPa. If it is less than the above, it tends to break at the time of processing or at the time of drawing after bonding with various sealants and the like, and at the time of dropping the bag, it may become easy to break the bag.
The upper limit of the MD breaking strength is preferably 300 MPa. If the above is exceeded, the effect of improving the breaking strength may be saturated.
In the biaxially stretched polyester film of the present invention, the lower limit of the TD breaking strength is preferably 160 MPa, more preferably 180 MPa, and further preferably 200 MPa. If it is less than the above, it tends to break at the time of processing or at the time of drawing after bonding with various sealants and the like, and at the time of dropping the bag, it may become easy to break the bag. MD breaking elongation can be made into the range with MD magnification and heat setting temperature.
The upper limit of the TD breaking strength is preferably 300. If the above is exceeded, the effect of improving the breaking strength may be saturated.
In the biaxially stretched polyester film of the present invention, the lower limit of the ratio between the MD breaking strength and the TD breaking strength is preferably 0.5, more preferably 0.7, and even more preferably 0.9. If it is less than the above, the deformation balance in the vertical and horizontal directions is biased at the time of drawing, and the thickness of the molded product may become uneven. The TD breaking elongation can be within the range by the MD magnification and the heat setting temperature.

The upper limit of the ratio of MD break strength to TD break strength is preferably 1.5, more preferably 1.3, and even more preferably 1.1. If the above is exceeded, the balance of deformation in the vertical and horizontal directions may be biased during drawing, and the thickness of the molded product may become non-uniform.

In the biaxially stretched polyester film of the present invention, the lower limit of MD breaking elongation and% is preferably 100%, more preferably 110%, and further preferably 120%. If it is less than the above, it may be disadvantageous in terms of workability such as drawing after bonding with various sealants.
The upper limit of MD break elongation is preferably 200%, and if it exceeds 200%, the improvement effect may be saturated.
The lower limit of the TD elongation at break is preferably 100%, more preferably 110%, and still more preferably 120%. If it is less than the above, it may be disadvantageous in terms of workability such as drawing after bonding with various sealants.
The upper limit of TD rupture elongation is preferably 200%. If it exceeds 200%, the improvement effect may be saturated.

In the biaxially stretched polyester film of the present invention, the lower limit of the ratio of MD break elongation to TD break elongation is preferably 0.5, more preferably 0.7, and even more preferably 0.9. . If it is less than the above, the deformation balance in the vertical and horizontal directions is biased at the time of drawing, and uniform molding cannot be performed, and breakage or pinholes may occur.
The upper limit of the ratio of MD break elongation to TD break elongation is preferably 1.5, more preferably 1.3, and even more preferably 1.1. If the above is exceeded, the balance of deformation in the vertical and horizontal directions is biased during drawing, and uniform molding cannot be achieved, and breakage and pinholes may occur.

In order to obtain a biaxially stretched polyester film having yield point stress, rupture strength, and rupture elongation within the above ranges, a method of laminating the same resin composition in a multilayer manner is preferable.

When the laminate obtained by laminating the biaxially stretched polyester film and the aluminum foil of the present invention is drawn, the lower limit of the drawing depth that can be formed uniformly and without breakage is preferably 5 mm or more, more preferably 5.5 mm or more. 6 mm or more is particularly preferable.
When the drawability exceeds 5 mm, it is suitable for draw forming for battery exteriors and the like.

The lower limit of the piercing strength of the biaxially stretched polyester film of the present invention is preferably 0.8 N / μm, more preferably 0.9 N / μm. If it is less than 0.8 N / μm, the strength at the time of processing or forming a bag may be insufficient. The upper limit of the piercing strength is preferably 1.5 N / μm, and if it exceeds 1.5 N / μm, the improvement effect is saturated. The piercing strength can be within the range by the MD magnification and the heat setting temperature.

The lower limit of the impact strength (impact resistance) of the biaxially stretched polyester film of the present invention is preferably 0.075 J / μm, more preferably 0.08 J / μm. When it is less than 0.075 J / μm, the strength may be insufficient when used as a bag. The upper limit of impact strength (impact resistance) is preferably 0.2 J / μm, and if it exceeds 0.2 J / μm, the improvement effect will be saturated.

The biaxially stretched polyester film of the present invention is more suitable for use as a packaging material or an exterior material by having the following film properties.

The lower limit of the MD elastic modulus of the biaxially stretched polyester film of the present invention is preferably 1 GPa, more preferably 1.2 GPa, still more preferably 1.4 GPa. If it is less than the above, it tends to be stretched and pitch deviation may occur during processing such as printing and lamination.
The upper limit of the MD elastic modulus is preferably 3 GPa, more preferably 2.8 GPa, and still more preferably 2.6 GPa. Exceeding the above may be disadvantageous in terms of workability such as drawing after bonding with various sealants.
The lower limit of the TD elastic modulus of the biaxially stretched polyester film of the present invention is preferably 1 GPa, more preferably 1.2 GPa, and further preferably 1.4 GPa. If it is less than the above, it tends to stretch and problems may occur during processing.
The upper limit of the TD elastic modulus is preferably 3 GPa, more preferably 2.8 GPa, and still more preferably 2.6 GPa. Exceeding the above may be disadvantageous in terms of workability such as drawing after bonding with various sealants.

The lower limit of the moisture absorption rate of the biaxially stretched polyester film of the present invention is preferably 0.1%, and if it is less than the above, the improvement effect will be saturated. The upper limit of the moisture absorption rate is preferably 1%, and if it exceeds the above, a change in moisture absorption dimension may easily occur.

In the biaxially stretched polyester film of the present invention, the lower limit of the MD heat shrinkage rate of the film is preferably 0.1%, and if it is less than the above, the improvement effect is saturated and it becomes mechanically brittle. There is. The upper limit of the MD thermal shrinkage is preferably 4%, and if it exceeds the above, pitch deviation may occur due to a dimensional change during processing such as printing.

The lower limit of the TD heat shrinkage rate of the biaxially stretched polyester film of the present invention is preferably 0.1%, and if it is less than the above, the improvement effect is saturated and it may become mechanically brittle. The upper limit of the TD heat shrinkage rate is preferably 3%, and if it exceeds the above, shrinkage in the width direction may occur due to a dimensional change during processing such as printing.

The haze of the biaxially stretched polyester film of the present invention is preferably 20% or less, more preferably 18% or less, further preferably 15% or less, and particularly preferably 10% or less. If it is less than the above, the transparency is poor and the appearance quality of the molded product may be lowered.

The lower limit of the number of pinholes generated by the gelboflex tester of the biaxially stretched polyester film of the present invention is preferably 0 (pieces, CPP lamination, after 2000 times). The upper limit of the gelbo is preferably 10 (pieces, CPP lamination, after 2000 times), more preferably 5 (pieces, CPP lamination, after 1000 times). If it exceeds 10 (pieces, CPP lamination, after 2000 times), holes may be easily formed when used as a bag.

Since the biaxially stretched polyester film of the present invention has low moisture absorption, the resulting distortion is small and the fragrance retention is excellent.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. The film was evaluated by the following measurement method.

[Film forming properties]
The film forming property of the biaxially stretched film was evaluated according to the following criteria. If it was (circle) and (triangle | delta), it was judged that productivity was good.
○: The film could be formed without breakage and continuous production was possible. Δ: The film-formability was somewhat unstable and the breakage occurred rarely, but it was a level where continuous production was possible.
X: Breaking frequently occurred and continuous production was difficult.

[Mechanical properties (yield stress value, initial elastic modulus, breaking strength, breaking elongation)]
According to JIS K 7113. A sample having a width of 10 mm and a length of 100 mm in the longitudinal direction and the width direction of the film was cut out using a razor as a sample. After standing for 12 hours in an atmosphere of 23 ° C. and 65% RH, the measurement was performed in an atmosphere of 23 ° C. and 65% RH under the conditions of a distance between chucks of 100 mm and a pulling speed of 200 mm / min. Values were used. As a measuring device, an autograph AG5000A manufactured by Shimadzu Corporation was used.

[Spherulite size]
The unstretched sheet obtained by casting was collected, and the Hv light scattering pattern of each unstretched sheet was measured using a light scattering measuring device (Otsuka Electronics: Dyna-3000). Using the Hv light scattering pattern obtained when the central angle of measurement was changed to 0 °, 20 °, and 60 °, the spherulite radius was determined from the spread of the scattering pattern. The unit is [nm].

[Thickness]
It was measured by a method according to JIS-Z-1702.

[Plane orientation]
A 10-point sample was taken from the roll sample in the width direction. According to JIS K 7142-1996 5.1 (Method A), the refractive index in the film longitudinal direction (nx), the refractive index in the width direction (ny), and the refractive index in the thickness direction using an Abbe refractometer with the sodium D line as the light source The ratio (nz) was measured, and the plane orientation coefficient (ΔP) was calculated by the following formula. In addition, the average value of the obtained plane orientation coefficient was made into the plane orientation coefficient.
ΔP = (nx + ny) / 2−nz
The difference in the plane orientation coefficient in the width direction was the difference between the maximum value and the minimum value of the above 10 samples.

[Drawing formability]
The obtained film roll and aluminum foil (8079 material, thickness 40 μm) were urethane adhesive (TM-509, CAT10L, Toyo Morton Co., Ltd., 33.6: 4.0: 62.4 (mass ratio). ) Was dry laminated to produce a film / aluminum foil laminate. The obtained laminate was placed in a die set mold (convex shape 90 mm × 50 mm) so that the polyester film was on the outside, and was pressed at 23 ° C. with a press to perform drawing. The drawing depth at the time of molding was increased by 0.2 mm, and the maximum depth at which the laminate was not damaged was taken as the drawing depth.

[Puncture strength]
It was measured in accordance with “2. Test methods for strength, etc.” in “Standards for Foods, Additives, etc. 3: Equipment and Containers and Packaging” in the Food Sanitation Law (Ministry of Health and Welfare Notification No. 20 of 1982). A needle having a tip diameter of 0.7 mm was pierced into the film at a piercing speed of 50 mm / min, and the strength when the needle penetrated the film was measured to obtain the piercing strength. The measurement is performed at room temperature (23 ° C.), and the unit is [N / μm].

[Impact strength]
Using an impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd., the strength against impact punching of the film in an atmosphere at 23 ° C. was measured. An impact spherical surface having a diameter of 1/2 inch was used. The unit is [J / μm].

[Heat shrinkage]
The thermal shrinkage of the polyester film was measured by the dimensional change test method described in JIS-C-2318 except that the test temperature was 150 ° C. and the heating time was 15 minutes.
The thermal shrinkage of the nylon film was measured by the dimensional change test method described in JIS-C-2318 except that the test temperature was 160 ° C. and the heating time was 10 minutes. The unit is [%].

[Haze]
The sample was measured at three different locations using a haze meter (Nippon Denshoku, NDH2000) by a method according to JIS-K-7105, and the average value was defined as haze.
The unit is [%].

[Pinhole resistance]
The film according to the present invention is cut into a size of 20.3 cm (8 inches) × 27.9 cm (11 inches), and the rectangular test film after the cutting is subjected to a condition of a temperature of 23 ° C. and a relative humidity of 50%. Conditioned for 24 hours or longer. Thereafter, the rectangular test film is wound to form a cylindrical shape having a length of 20.32 cm (8 inches). Then, one end of the cylindrical film is fixed to the outer periphery of a disk-shaped fixed head of a gelbo flex tester (manufactured by Rigaku Kogyo Co., Ltd., NO.901 type) (conforming to MIL-B-131C standard). The other end of the tester was fixed to the outer periphery of a disk-shaped movable head of a tester facing the fixed head at a distance of 17.8 cm (7 inches). Then, the movable head is rotated 440 ° while approaching the fixed head in the direction of 7.6 cm (3.5 inches) along the axis of both heads opposed in parallel, and then 6.4 cm (without rotation) 2.5-inch) A one-cycle bending test in which the movement is performed in the reverse direction and the movable head is returned to the initial position is performed continuously for 2000 cycles at a rate of 40 cycles per minute. Repeated. Implementation was at 5 ° C. Thereafter, the number of pinholes generated in a portion within 17.8 cm (7 inches) × 27.9 cm (11 inches) excluding the portion fixed to the outer periphery of the fixed head and the movable head of the tested film was measured (ie, The number of pinholes per 77 square inches was measured).

[Example 1]
Using a single screw extruder, add a masterbatch containing PBT (Mitsubishi Engineering Plastics Novaduran 5020, melting point 220 ° C.) and calcium carbonate as a lubricant as a polyester resin composition (A), and blend to a lubricant concentration of 2000 ppm. The melted product was melted at 270 ° C., and then the melt line was introduced into a 12-element static mixer. Thereby, the PBT melt was divided and laminated to obtain a multilayer melt made of the same raw material. It was cast from a T-die at 270 ° C. and adhered to a cooling roll at 10 ° C. by an electrostatic adhesion method to obtain an unstretched sheet. When the surface temperature of the cooling roll was measured at 10 cm intervals in the width direction (thermocouple), the variation was 3 ° C. or less. Next, the film was stretched 3.2 times in the machine direction at 60 ° C., then stretched 3.9 times in the transverse direction at 80 ° C. through a tenter, tension heat treatment at 200 ° C. for 3 seconds and 3% in 1 second. After the relaxation treatment, both end portions were cut and removed to obtain a PBT film having a thickness of 12 μm.
Table 1 shows the film forming conditions, physical properties, and evaluation results of the obtained film.

[Examples 2 to 9]
In Example 1, it carried out like Example 1 except having changed the raw material composition and the film forming conditions into the biaxially stretched film described in Table 1.
(PBT: Mitsubishi Engineering Plastic Novaduran 5020, melting point 220 ° C.) (ecoflex: manufactured by BASF, polybutylene adipate butylene terephthalate copolymer)
(GS390: manufactured by Toyobo Co., Ltd., copolymerization component: polybutylene terephthalate, polycaprolactone)
Table 1 shows the film forming conditions, physical properties, and evaluation results of the obtained film.

[Comparative Examples 1 to 4]
In Example 1, it carried out like Example 1 except having changed the raw material composition and the film forming conditions into the biaxially stretched film described in Table 2.
(PBT: Mitsubishi Engineering Plastic Novaduran 5020, melting point 220 ° C.) (ecoflex: manufactured by BASF, polybutylene adipate butylene terephthalate copolymer)
Table 2 shows the film forming conditions, physical properties, and evaluation results of the obtained film.

[Comparative Example 5]
PBT (Mitsubishi Engineering Plastics Novaduran 5020, melting point 220 ° C.) and polyethylene terephthalate (intrinsic viscosity 0.65) are used as the polyester resin, and PBT and PET are melted at 280 ° C. using an extruder, respectively. To obtain a PBT / PET alternating multilayer melt. This alternate laminate was cast from a die at 280 ° C. and adhered to a cooling roll at 20 ° C. by an electrostatic adhesion method to obtain an unstretched sheet. The obtained unstretched sheet was biaxially stretched under the film forming conditions shown in Table 2 to obtain a PBT / PET alternately laminated biaxially stretched film.
The physical properties and evaluation results of the obtained film are shown in Table 2.

[Comparative Example 6]
PBT (Mitsubishi Engineering Plastics Novaduran 5020, melting point 220 ° C) is used as the polyester resin, melted at 280 ° C using a single screw extruder, cast from a 270 ° C die, and electrostatically attached to a 15 ° C cooling roll. It was made to adhere and the unstretched sheet was obtained. The film was formed by adjusting the winding speed so that the thickness was 20 μm.
The physical properties and evaluation results of the obtained film are shown in Table 2.

[Comparative Example 7]
The thing made by the Kansai Chemical Industrial PBT film company marketed as a typical inflation biaxially-stretched PBT film was used.
The physical properties and evaluation results of the obtained film are shown in Table 2.

[Comparative Example 8]
An ester film E5100-12 μm manufactured by Toyobo was used.
The physical properties and evaluation results of the obtained film are shown in Table 2.

[Comparative Example 9]
A nylon film N1100-15 μm manufactured by Toyobo was used.
The physical properties and evaluation results of the obtained film are shown in Table 2.

According to the present invention, it is possible to obtain a biaxially stretched polyester film suitable for uses such as retort food packaging applications and draw forming such as lithium ion battery exterior materials, in which nylon films and other flexible films have been used. It is expected to contribute greatly to the industry.

Claims

It consists of a polyester resin composition (A) containing 60% by mass or more of polybutylene terephthalate. The yield point stress of MD is 70 MPa or less, the yield point stress of TD is 70 MPa or less, the fracture strength of MD is 160 MPa or more, and the fracture strength of TD is A biaxially stretched polyester film characterized by having a breaking elongation of 160 MPa or more and MD and TD of 100% or more.
The biaxially stretched polyester film according to claim 1, wherein the polyester resin (A) comprises a polyester resin (B) other than polybutylene terephthalate.
3. The biaxial stretching according to claim 1, wherein the biaxial stretching is obtained by biaxially stretching an unstretched polyester sheet having a thickness of 15 to 2500 μm cast after multilayering the same composition into 60 layers or more. A method for producing a polyester film.
3. The biaxially stretched polyester film according to claim 1, wherein the unstretched polyester sheet is obtained by bringing a non-stretched polyester sheet into contact with a chill roll of 20 ° C. or less and cooling and then biaxially stretching.
3. The method for producing a biaxially stretched polyester film according to claim 1, wherein the unstretched polyester sheet is obtained by biaxially stretching an unstretched polyester sheet having a spherulite diameter of 500 nm or less.
The ratio of the breaking strength of the MD and the breaking strength of the TD is 1.5 or less, and the ratio of the breaking elongation of the MD and the breaking elongation of the TD is 1.5 or less. Axial stretched polyester film.
The method for producing a biaxially stretched polyester film according to any one of claims 4 to 6, which is obtained by sequentially biaxially stretching the unstretched polyester sheet.